Hair dye compositions of the prior art include oxidizing type hair dyes that perform dyeing using an oxidation-reduction reaction, and acid hair dyes that perform dyeing in the acidic region using a dye prescribed by law. Among these, the main ingredients of acid hair dyes consist of acid dyes, alcohols (typically benzyl alcohol), organic solvents and a pH-controlling acids (typically citric acid). These are formulated with a thickener so as to prevent the dye from running off the hair during use. Since these hair dye compositions normally involve single preparations, they have the advantage of being easier to use compared with oxidizing hair dyes that require two or more preparations. However, the optimum pH range of acid hair dyes is 1.5-4.5 (Note: this range is preferable for obtaining favorable dyeing properties and washability, with an average pH range of around 3 being preferable). Since this pH is considerably low with respect to ordinary cosmetic products for the hair, this type of hair dye composition has a disadvantage in that it often imparts an unsatisfactory feeling during application thereof.
On the other hand, as acid hair dyes are single preparations, a possible application that takes advantage of that characteristic is a combined rinse and hair dye composition usable after shampooing. In addition, in the case of such a composition, both rinsing and dyeing can be performed simultaneously, making it extremely useful as an easy-to-use, convenient hair dye preparation. In order to realize a combined rinse and hair dye composition, it is necessary that the composition contain a small but sufficient amount of dyes so that the dyes do not remain on the hands after shampooing. However, when the amount of dyes is simply reduced, the dyeing properties become inadequate whereby the composition is prevented from demonstrating its initial effects.